1. Field of the Invention
The present invention relates to an ink-jet printing apparatus and an ink-jet printing method and, more specifically, to an ink-jet printing apparatus and an ink-jet printing method for performing printing, by insolubilizing or coagulating a color component contained in the ink, onto a printing medium.
2. Description of the Related Art
An ink-jet printing system is widely employed in printing apparatuses, copying machines, facsimile machines and so forth because its advantages in lowering noise, reducing running costs, and facilitating the miniaturization of apparatuses and the design of color printing apparatuses.
Most conventional ink-jet printing systems employ a special printing sheet provided with a waterproof ink absorbing layer to secure satisfactory water-resistance of the ink thereon and to print a color image of high coloring without bleeding of ink. Recent improvement of ink has increased the printability of an ordinary printing sheet, which is used in large quantities in printing apparatuses, copying machines and the like. However, the print quality of images printed on the ordinary printing sheets is not yet perfectly satisfactory. There have been some proposals, to improve the water-resistance property of the ordinary printing sheet and to improve printing quality.
As one method of improving the water-resistance property of the image through the improvement of ink, for example, a method of making a coloring component in the ink have the water-resistance property is known. This prior method, however, uses an ink which barely becomes soluble to water after drying. Therefore, an ejection opening of an ink-jet head using such an ink is liable to be clogged with dried ink. In addition, although it is possible to realize structure for preventing the ejection openings from being clogged, a problem that the structure requires a complex mechanism occurs.
In Japanese Patent Application Laid-open No. 84992/1981, there is disclosed a method which uses a printing medium coated with a dye fixing material. This prior method, however, needs to use a special printing medium capable of being coated with the dye fixing material, needs to use a large apparatus for coating the printing medium with the dye fixing material, and, unavoidably, increases the cost of the apparatus. Furthermore, it is comparatively difficult to coat the printing medium with a film of the dye fixing material having a predetermined thickness.
To improve printing quality, it is required that 1) characters and images must be sharply printed without occurring irregular blurring of ink on an edge of ink dots (hereinafter referred to as "feathering"), and that 2) an image is clearly printed without bleeding, i.e., without mixing of inks occurring on a boundary between adjacent regions of respective different colors. The ink must be prevented from permeating the printing medium to prevent feathering stated at article 1). In such case, however, aqueous inks, which are used by common ink-jet printing systems, are liable to cause bleeding stated at article 2). In contrast, in the case of facilitating the permeation of the ink into the printing medium, feathering is enhanced although bleeding stated at article 2) can be reduced.
In order to solve a problem set forth above, there is proposed, in Japanese Patent Application Laid-open No. 63185/1989 and Japanese Patent Application Laid-open No. 249755/1986, methods in which a clear liquid that insolubilizes the dye contained in the ink is deposited together with the ink on the printing medium by an ink-jet head.
According to methods stated above, the colored ink deposited on the printing medium is insolubilized to be fixed on the printing medium and hence a high water-resistance property of the printed product can be obtained. Both feathering and bleeding can be suppressed by applying a clear processing liquid to the printing medium under given conditions prior to ejecting ink on the printing medium.
On the other hand, there are known an ink-jet printing method of a multi-scanning system disclosed in Japanese Patent Application Laid-open Nos. 358847/1992 and 155036/1993 and an ink-jet printing method of a multi-pass system disclosed in Japanese Patent Application Laid-open No. 207665/1991 in which a plurality of scanning cycles of an ink-jet head are effected along a scanning direction to form one line of pixels. According to an above described method, one line of pixels is formed by ink droplets ejected through a plurality of different ejection openings. Therefore, variations among the ejection openings in ejection volume and an ejecting direction are averaged, so that density unevenness and misdirected landings are not liable to occur and high-quality printing can be realized.
Incidentally, the use of the aforesaid processing liquid in the foregoing multi-scanning system entails the following problems.
In this case that the processing liquid is ejected once for one ink ejecting cycle as mentioned in Japanese Patent Application Laid-open No. 63185/1989, the processing liquid is deposited in overlapping manner in the multi-scanning system, so that an excessive quantity of the processing liquid may be applied to the printing medium. As a result of this, the printing medium to which the excessive processing liquid is applied becomes cockled state which makes the surface of the printing medium rugged. And the cockled printing medium interferes with the ink-jet head and the internal components of the printing apparatus, and the cockled printing medium may possibly cause jamming and smear the printed printing medium with the ink. In some cases, the image printed on the printing medium is difficult to see and printing quality is deteriorated when the cockled printing medium dries in a cockled state.
Furthermore, since such a mode of printing consumes a large quantity of the processing liquid, a tank containing the processing liquid needs to be changed or to be replenished with the processing liquid frequently, the running cost is increased, and the load on the user increases. In case that a tank having an increased size is used to save work for changing the tank, the size of the printing apparatus needs to be increased, a cost of the printing apparatus is increased, and an operability of the printing apparatus is spoiled.
A method of reducing a deposition amount of the processing liquid is proposed in, for example, Japanese Patent Application Laid-open No. 128862/1983. In this document, when printing with a plurality of kinds of inks, data for ejecting the processing liquid is generated by carrying out logical OR between data for ejecting respective inks of colors. According to a method set forth above, when performing printing of R (red) by ejecting one Y ink (Yellow) droplet and one M ink (magenta) droplet, one processing liquid droplet for each of the Y- and the M-ink droplets is not ejected but only one processing liquid droplet is ejected. An effect of ejecting only one processing liquid droplet for two ink droplets in preventing feathering and bleeding is scarcely different from that of ejecting two processing liquid droplets for two ink droplets, the water resistance is improved effectively, and consumption of the processing liquid is reduced by 1/2 to 1/3 the consumption of the same by the conventional method. Even if this method is employed, however, the consumption of the processing liquid, as compared with the consumption of the ink, is considerably large.
Suppose that a full-color image is printed with, for example, Y-ink (yellow ink), an M-ink (magenta ink), a C-ink (cyan ink) and a Bk-ink (black ink) by employing the aforesaid method which carries out logical OR between the data for ejecting respective inks, the amount of the processing liquid required for printing a primary color portion, a second color portion and a third color portion is equal to, 1/2 and 1/3 the total amount of the inks for printing the primary color portion, the second color portion and the third color portion, respectively. In such case, suppose that an image to be printed consists of the primary color patterns of the four color inks having the same area, the second color patterns of six colors of the four color inks having the same area, or the third color patterns of the four color inks having the same area, the amount of the processing liquid necessary for printing the image is four times, two times or about 1.3 times the amount of each of the four color inks, respectively. Although one cannot make that kind of sweeping generalization because different images have different ratios in area between the primary color, the second color and the third color patterns, the amount of the processing liquid necessary for printing an image is, on an average, two to three times the amount of each color ink necessary for printing the same image.